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How To - Make A Balsa Strop

1. INTRODUCTION

Balsa strops are used with cutting compounds in the final progressions of blade edge preparation. They are normally hand-held and the blade is stropped on the pasted balsawood similar to stropping on a leather strop (the progression finale).

2. OVERALL SIZE (Don’t believe her, size does matter)

2.1 WIDTH
The balsa strop arrangement needs to (preferably) be wide enough to accommodate the length of your blade edge plus a little. If it is not wide enough, you can use the extended “X” method of stropping. Most blade edges are about 70mm (2 ¾”) long so a width of about 75mm (3”) can be ideal. If you normally use longer blades, a wider strop arrangement may be preferred. Remember though that the strop is to be hand-help so anything over about 85mm (3 ½”) may be difficult to hold.

2.2 LENGTH
The balsa strop needs to be long enough to comfortably strop upon while hand-held. If it is too long, it will be difficult to establish a good stropping technique. If too short, you will need to perform more stropping laps to achieve the same result. Balsa generally comes in lengths of about 900mm (36”) so most people appear to be happy with a balsa strop length of about 300mm (12”). Under 250mm (10”) length is getting too short and over about 450mm (15”) is getting too long.

3. THE PARTS

3.1 GENERAL

There are two main parts to the balsa strop; the balsawood and the substrate.

Balsawood
The balsawood needs to be clear and straight grained with a smooth and relatively flat surface on each side. A minimum thickness of 5mm (3/16”) is required however most prefer to work with anything from 6mm (¼”) to 12mm (½”) thickness. The thicker the balsawood the longer it will last you with multiple lapping to reset it flat. The thicker it is the more times it will need to be lapped flat due to the thickness expanding and contracting with humidity.

Substrate
The substrate needs to perform four functions:
  • Be of a size to provide support for the full length and width of the balsawood.
  • Provide a flat sold non-flexible base for the balsawood so as to minimise the balsawood warping and bending.
  • Be of sufficient thickness to prevent damaging your delicate manicure from the blade while stropping in hand. The preferred thickness will vary from person to person. A thickness of about 20mm (¾”) plus balsawood thickness seems to suit most people however some are happy with only 15mm (⅝”) while others prefer up to 25mm (1”).
  • To have relatively low mass (weight) so as to not fategue the user during use.
Some suitable substrates are:

Acrylic Sheet: There are two main types available, extruded and cast. Cast is better to use if available as it tends to not crack as easily from edge imperfections.
Relative Density = 1.18

Aluminium Alloy: Here you can use either rolled plate or extruded bar. If rolled plate, grade 5083 H321 is recommended. If extruded bar, grade 6061 T6 is recommended. Both of these grades offer good corrosion resistance and high stiffness. Other grades may also be suitable.
Relative Density = 2.7

Composite: This can be the cheapest substrate.The top can be a smooth glazed tile (about 6mm or ¼” thick) cut to size using an angel grinder with diamond disc. Onto the underside of the tile you glue (epoxy glue recommended) marine plywood (cheapest) or a closed cell structural foam (lightest) to your desired thickness.
Relative Density = 0.85 to 1.4

4. PUTTING IT ALL TOGETHER

If using a composite substrate, wait at leat 24 hours for the glue to fully set. Use a rubber glue to bond your balsawood to the substrate. Rubber glue is preferred as it allows you to later remove and replace the balsawood without damaging the top surface of your substrate. Other types of glues may be used if you so desire.

Apply some weight(s) to hold the join between the balsa and substrate in close contact. For rubber glue allow at least 24 hours for the glue to set.

Once the glue is fully set, use a flat smooth lapping plate and a sheet of sandpaper (about 320 grit) to lap the top surface of your balsawood perfectly flat. This is best done using the cross-hatch pencil method.

With the top surface of your balsawood now perfectly flat, you need to remove any loose pieces of balsawood (dust). This can be done using compressed air or a vacuum cleaner suction with a brush nozzle.

Your balsa strop is now ready for pasting.

5. EXAMPLES

Composite

300mm (12”) x 75mm (3”). 2 x 8mm structural foam + 1 x 6mm glazed tile + 10mm balsawood

IMG_20200119_143249.jpg
 
I would have preferred to have this in the shavewiki but I am not yet sure how to do that. Perhaps a modie could help.

It then could be easily edited as needed.
 
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Read through this completely, all your questions should be answered. All the way to the end.
 
Materials can be sourced as follows:

Balsawood

Most hobby shops or online (generally at a higher price).

Acrylic

Not sure where for thick acrylic. Try glazing supplies. If they do not have it, they might be able to point you in the right direction.

Glazed Tiles

Most of the larger home improvement stores.

Aluminium

Most of the larger aluminium metal merchants.

Timber/Plywood

Most timber merchants.

Glues

Your local hardware store.

Diamond Lapping Paste

Try the Bay or similar.
 
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Read through Slash's "How To Use A Pasted Balsa Strop" completely, all your questions should be answered. All the way to the end.
True, however it can be a long read. This thread is not meant to replace Slash's excellent and detailed instructions on using a pasted balsa strop. It is merely consolidating one small part of his thread so as to assist others in making their hand-held balsa strops.
 
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www.tapplastics.com I think is the url for TAP Plastics.
Cast Acrylic Sheets Cut-To-Size : TAP Plastics - https://www.tapplastics.com/product/plastics/cut_to_size_plastic/acrylic_sheets_cast_clear/510 for the right stuff. 3/4" x 3" x 12" with no options, 2 pcs is $18.35. One piece is $10 cause a $10 minimum order. Upgrade to 1" thick for $14.27.

Ted Pella is the final word in diamond paste quality. But yeah, the Chinese stuff on fleabay actually seems to work nearly as good.
 

Seveneighth

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www.tapplastics.com I think is the url for TAP Plastics.
Cast Acrylic Sheets Cut-To-Size : TAP Plastics - https://www.tapplastics.com/product/plastics/cut_to_size_plastic/acrylic_sheets_cast_clear/510 for the right stuff. 3/4" x 3" x 12" with no options, 2 pcs is $18.35. One piece is $10 cause a $10 minimum order. Upgrade to 1" thick for $14.27.

Ted Pella is the final word in diamond paste quality. But yeah, the Chinese stuff on fleabay actually seems to work nearly as good.
If you are buying the chinese stuff it's worth trying a couple of sources. My first purchase was not good.
 
TAP Plastics is a US company with several brick and mortar outlets and I think their products are made in house in the US. Maybe not? Anyway everything I have ever got from them was top notch. Good source of 1/8" colored translucent or opaque acrylic for scales, too. Were you disappointed in something you got from them?
 
Maybe a stupid question, but thought I’d ask - would 1/4” MDF work in place of balsa? I ask because I have quite a bit of MDF left over from an amplifier-building project. Lap it, glue it to glass/acrylic/tile base?
 
Maybe a stupid question, but thought I’d ask - would 1/4” MDF work in place of balsa? I ask because I have quite a bit of MDF left over from an amplifier-building project. Lap it, glue it to glass/acrylic/tile base?
Not really a stupid question at all, if your reason for asking it was to learn. But what sort of results are you seeking? If you want Method results, follow The Method. If you want MDF results, use MDF. MDF might improve the edge, but PROPERLY SET UP AND PROPERLY USED balsa will improve it more. There are plenty of reasons to use different things or different techniques, so do go ahead and try it, but I would urge you to then try balsa, properly prepared, and see the difference for yourself. I can hone a razor on a brick, but I won't, and I won't recommend it to others, either. It won't deliver best possible results. And best possible results IMHO are the only results worth seeking.
 
For a lighter weight composite balsa strop, you can replace the timber/plywood under the tile with balsa wood. Not the cheapest of timbers but normally readily available.
 
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